The ability to switch a logic gate through control of electron spin is the fundamental concept underlying spintronic logic circuits. By using electron spin along with charge, new avenues for manipulating signal flow become available [1]. It is therefore possible to develop logic devices with additional capabilities that are more efficient, leading to logic circuits with improved characteristics [2].
While electron spin has already found applications for computing in memory structures such as hard drives and magnetoresistive random-access memory (MRAM), the difficulty in cascading these devices has prevented its integration into logic structures. With the exception of the spin-diode logic family [3], the capability of driving the input of one spin-based logic gate with the output of a second spin-based logic gate has not been shown without requiring additional control logic. This ability to cascade gates is a fundamental requirement of logic circuits, and is a primary challenge for spin-based logic.
Originally, Datta and Das proposed a field effect transistor in which a gate voltage controls the spin-precession of electrons moving between the source and drain [4]. This work inspired the utilization of the spin degree of freedom, resulting in several distinct techniques. One prominent technique uses a current-carrying wire to create a magnetic field in a two-terminal device to switch between a conductive and resistive state. This technique has been suggested for logic based on magnetic tunnel junctions [5], [6] and magnetoresistive semiconductor heterojunctions [7], and is currently used in MRAM [2], [8]. Magnetic quantum cellular automata logic, in which localized spin states are used to control nearby spin states [9], [10], and magnetic domain-wall logic, in which a rotating magnetic field induces motion of magnetic domains in nanowires [11], are alternative techniques that have been demonstrated in circuits at room temperature. Logic based on spin accumulation [12], spin-wave phase [13], and spin-torque [14], [15], have also been proposed.
An unaddressed need exists in the art to address the deficiencies and inadequacies identified above.